(a) Field of the Invention
The present invention relates to a plastic film. More particularly, the present invention relates to a plastic film exhibiting a high level of hardness and excellent processability.
This application claims the benefit of Korean Patent Application No. 10-2013-0028141, filed on Mar. 15, 2013, and Korean Patent Application No. 10-2014-0029033, filed on Mar. 12, 2014, which are both hereby incorporated by reference in their entireties into this application.
(b) Description of the Related Art
With the advance of mobile appliances such as smart phones, tablet PCs and the like, further lightness and thinness have recently been required of substrates for displays. Display windows or front panels of such mobile appliances are generally made of glass or reinforced glass both of which have excellent mechanical properties. However, glass suffers from the disadvantage of increasing the weight of mobile appliances and is easily broken by external impact.
As an alternative to glass, plastic resins have been studied. Their light weight and resistance to impact are consistent with the trend of pursuing lighter and thinner mobile appliances. Particularly, a film with high hardness and wear resistance is required. In this regard, the utilization of a structure in which the substrate is coated with a coating layer has been proposed.
First of all, increasing the thickness of the coating layer is considered a possible approach to improving the surface hardness thereof. In fact, the coating layer should be of a minimal thickness to ensure the surface hardness of the coating layer. As the coating layer increases in thickness, the surface hardness thereof may become higher. However, a thicker coating layer, although increasing the surface hardness, is more prone to setting shrinkage, which leads to wrinkling or curling with the concomitant production of cracks or exfoliations, and thus thick coating layers are difficult to employ in practice.
Recently, several methods have been proposed for conferring a high hardness to plastic films, without the problems of cracking and setting shrinkage-induced curling.
Korean Patent Application Publication No. 2010-0041992 discloses a plastic film composition, free of monomers, comprising a binder resin based on ultraviolet-curable polyurethane acrylate oligomers. However, this plastic film has a pencil hardness of about 3H, and thus the strength thereof is insufficient to be a substitute for glass panels for displays.